Image forming apparatus

Abstract

In a cross section perpendicular to a rotational axis of a first image bearing member, when a common tangential line between the first image bearing member and a second image bearing member on an intermediary transfer belt side is a rectilinear line L, a rectilinear line passing through a rotation center of the first image bearing member and a rotation center of a first transfer member is a rectilinear line P, and a rectilinear line passing through an intersection point between the rectilinear line P and the first image bearing member and perpendicular to the rectilinear line P is a rectilinear line Q, an electrode member is constituted so that the contact portion contacting an inner surface of the belt is positioned on a first image bearing member side than the rectilinear line L is and on a first transfer member side than the rectilinear line Q is.

What is claimed is: 
     
         1 . An image forming apparatus comprising:
 a first image bearing member configured to bear a toner image;   a second image bearing member configured to bear a toner image;   an intermediary transfer belt onto which the toner images are transferred from the first image bearing member and the second image bearing member, wherein the first image bearing member is provided adjacent to the second image bearing member on a side upstream of the second image bearing member with respect to a movement direction of the intermediary transfer belt;   a first transfer member provided downstream of the first image bearing member with respect to the movement direction of the intermediary transfer belt and configured to transfer the toner image from the first image bearing member onto the intermediary transfer belt in a first transfer portion under application of a first transfer voltage;   a second transfer member provided downstream of the second image bearing member with respect to the movement direction of the intermediary transfer belt and configured to transfer the toner image from the second image bearing member onto the intermediary transfer belt in a second transfer portion under application of a second transfer voltage; and   an electrode member provided downstream of the first transfer portion and upstream of the second transfer portion with respect to the movement direction of the intermediary transfer belt and includes a contact portion contacting an inner surface of the intermediary transfer belt, wherein a voltage of a polarity opposite to a polarity of the first transfer voltage is applied to the electrode member,   wherein in a cross section perpendicular to a rotational axis of the first image bearing member, when a common tangential line between the first transfer member and the second image bearing member on an intermediary transfer belt side is a rectilinear line L, a rectilinear line passing through a rotation center of the first image bearing member and a rotation center of the first transfer member is a rectilinear line P, and a rectilinear line passing through an intersection point between the rectilinear line P and the first image bearing member and perpendicular to the rectilinear line P is a rectilinear line Q, the electrode member is configured so that the contact portion is positioned on a first image bearing member side than the rectilinear line L is and on a first transfer member side than the rectilinear line Q is.   
     
     
         2 . An image forming apparatus according to  claim 1 , wherein in the cross section perpendicular to the rotational axis direction of the first image bearing member, in a perpendicular direction perpendicular to a direction along a common tangential line between the first image bearing member and the second image bearing member, an entering amount of the contact portion into the rectilinear line L is 5% or more and 80% or less when the entering amount is 100% when the contact control enters to the rectilinear line Q. 
     
     
         3 . An image forming apparatus according to  claim 1 , wherein in the cross section perpendicular to the rotational axis direction of the first image bearing member, in a perpendicular direction perpendicular to a direction along a common tangential line between the first image bearing member and the second image bearing member, an entering amount of the contact portion into the rectilinear line L is 10% or more and 50% or less when the entering amount is 100% when the contact portion enters to the rectilinear line Q. 
     
     
         4 . An image forming apparatus according to  claim 1 , wherein the contact portion contacts an inner peripheral surface of the intermediary transfer belt at a surface thereof. 
     
     
         5 . An image forming apparatus according to  claim 1 , wherein the contact portion is a flat surface. 
     
     
         6 . An image forming apparatus according to  claim 1 , wherein the contact portion is a curved surface convex toward the first image bearing member. 
     
     
         7 . An image forming apparatus according to  claim 1 , wherein a length of the contact portion in the movement direction of the intermediary transfer belt is 5 mm or more and 50 mm or less. 
     
     
         8 . An image forming apparatus according to  claim 1 , wherein a length of the contact portion in the movement direction of the intermediary transfer belt is not more than a half of a center distance between the first image bearing member and the second image bearing member in a cross section substantially perpendicular to a widthwise direction of the intermediary transfer belt. 
     
     
         9 . An image forming apparatus according to  claim 1 , wherein the contact portion is formed with an electroconductive material. 
     
     
         10 . An image forming apparatus according to  claim 9 , wherein the contact portion is formed with electroconductive metal. 
     
     
         11 . An image forming apparatus according to  claim 9 , wherein the contact portion is formed with electroconductive fibers. 
     
     
         12 . An image forming apparatus according to  claim 1 , wherein the electrode member includes a non-electroconductive supporting portion for supporting the contact portion, and the supporting portion is provided so as to contact the intermediary transfer belt on a side upstream of the contact portion with respect to the movement direction of the intermediary transfer belt. 
     
     
         13 . An image forming apparatus according to  claim 1 , further comprising an urging member configured to urge the electrode member from a rear surface of the electrode member in a direction toward the intermediary transfer belt so that the contact portion contacts an inner peripheral surface of the intermediary transfer belt. 
     
     
         14 . An image forming apparatus according to  claim 13 , wherein the urging member is formed with a spring, a sponge, or a nonwoven fabric, which is elastically deformable.